Titanium oxide (TiO2) is a potential photocatalyst for removing toxic NOx from the atmosphere. Its practical application is, however, significantly limited by its low absorption into visible light and a high degree of charge recombination. The overall photocatalytic activity of TiO2 remains too low since it can utilize only about 4–5% of solar energy. Nitrogen doping into the TiO2 lattice takes advantage of utilizing a wide range of solar radiation by increasing the absorption capability towards the visible light region. In this work, N-doped TiO2, referred to as TC, was synthesized by a simple co-precipitation of tri-thiocyanuric acid (TCA) with P25 followed by heat treatment at 550 degrees C. The resulting nitrogen doping increased the visible-light absorption and enhanced the separation/transfer of photo-excited charge carriers by capturing holes by reduced titanium ions. As a result, TC samples exhibited excellent photocatalytic activities of 59% and 51% in NO oxidation under UV and visible light irradiation, in which the optimum mass ratio of TCA to P25 was found to be 10.

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A simple spectrophotometric method was developed to quantify chlorophenol (CP) concentrations after reaction with potassium permanganate and quenching with sodium sulfite. Other quenching agents (peroxide, sodium thiosulfate and hydroxylamine hydrochloride) were found to create absorbance in the spectral range required for CP quantification. Analysis at pH 12 gave greater absorption and sensitivity for the method compared with pH 5.6. The calibration curves of the proposed methods were linear in the concentration ranges 0.0061-0.61 and 0.0078-0.78 mM with detection limit of 0.0006 and 0.0008 mM for dichlorophenols and monochlorophenols, respectively. The oxidation kinetics of five chlorophenols in aqueous solution with excess potassium permanganate were evaluated using the analytical method. The pseudo-first-order reaction rates were found to be relatively rapid 1.42× 10 −3 to 0.024 s −1 and followed the sequence 2-chlorophenol (2-CP) > 2,6-dichlorophenol (2,6-DCP)> 4-chlorophenol (4-CP) > 2,4-dichlorophenol (2, 4-DCP)>3-chlorophenol (3-CP). The apparent second-order rate constant was calculated from the measured pseudo-first-order rate constant with respect to CP with initial KMnO 4 concentration (1.5 mM) and follows the same sequence of pseudofirst-order rate constant. This shows that chlorine atoms in the structure of chlorophenol had a significant influence on the oxidation of chlorophenols by potassium permanganate. Permanganate can be used for the treatment of chlorophenolcontaminated soil and groundwater.

In this study, anatase titania was utilized to prepare a durable photocatalytic paint with substantially enhanced photoactivity towards NO oxidation. Consequently, to alleviate the choking effect of photocatalytic paint and incorporate self-cleaning properties, the parent anatase titania was modified with Al(OH)3 and a number of organosilane (tetraethyl orthosilicate, propyltrimethoxysilane, triethoxy(octadecyl)silane, and trimethylchlorosilane) coatings. A facile hydrolysis approach in ethanol was employed to coat the parent titania. To facilitate uniform dispersion in photocatalytic paint and strong bonding with the prevailing organic matrix, it is necessary to avail both hydrophobic and hydrophilic regions on the titania surface. Therefore, during the preparation of modified titania, the weight proportion of the total weight of alkyl silane and trimethylchlorosilane was adjusted to a ratio of 1:1. As the parent titania has few hydrophilic portions on the surface, tetraethyl orthosilicate was coated with an organic silane having an extended alkyl group as a hydrophobic group and tetraethyl orthosilicate as a hydrophilic group. When these two silane mixtures are hydrolyzed simultaneously and coated on the surface of parent titania, a portion containing a large amount of tetraethyl orthosilicate becomes hydrophilic, and a part containing an alkyl silane becomes hydrophobic. The surface morphology and the modified titania’s optical attributes were assessed using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), UV-Vis diffuse reflectance spectroscopy (DRS), and electrochemical impedance spectroscopy (EIS) analysis. Based on the advanced characterizations, the NO removal mechanism of the modified titania is reported. The modified titania coated at 20 wt.% on the ceramic substrate was found to remove ~18% of NO under one h of UV irradiation. An extensive UV durability test was also carried out, whereby the coated surface with modified titania was exposed to 350 W/m2 of UV irradiance for 2 weeks. The results indicated that the coated surface appeared to preserve the self-cleaning property even after oil spraying. Hence, facile hydrolysis of multiple organosilane in ethanol could be a viable approach to design the coating on anatase titania for the fabrication of durable photoactive paint.

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